The AC on my 2002 Chevy Cavalier stopped blowing cold in the fall and I had planned on getting it checked out and recharged once the AC check specials started. I saw this for $30 and it seems too good to be true. Do they work? Anything I should look out for?

3 Answers
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If your low on freon, there may be a leak. However, if this is the case use a bottle of stop leak first or a bottle mixed with stop leak. It should seal up an value leakage. Replacing your AC unit is costly, most leaks can be fixed with a stop leak sealant unless the problem is serious.

Save the hose you can reuse it.

Look for sales.

Don't expect to use half the bottle. Buy what you need. This is because once you pull the hose off the can can't be resealed.

Usually 2 of the small cans is enough to completely refill the AC unit.

Procedure.

Screw on the cap and tighten down the gauge, it will poke a hole in the bottle.

Attach the hose to the low pressure air conditioning value. There are 2 AC lines, one high, one low pressure. They're both metal. Open the low pressure one and attach the hose well.

Loosen the gauge and let the material flow from the bottle into the AC lines.

Start up the car and crank up the AC

Tilt the can upside down periodically.

Close the gauge by tighting it down on the bottle. When you do that you can read the pressure in the AC lines.

It's perfectly reasonable to use half the bottle. I have a half-full bottle which is almost a year old. I can tell it hasn't leaked because of the weight, and it sloshes when shaken. As my answer mentions, I'm not using a "freebie" hose. (Why would you want to remove the hose from the bottle?)
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PotatoswatterMay 26 '11 at 11:33

@Potatoswatter If you save the hose, you can use it with another can.
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Mark Johnson♦May 28 '12 at 16:09

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@MarkJohnson I was responding to the part "Don't expect to use half the bottle. Buy what you need. This is because once you pull the hose off the can can't be resealed." — it's silly to pull the hose off and let out all the gas, and reasonable to use only half the bottle.
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PotatoswatterMay 28 '12 at 16:23

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@endolith The shaking and rotating is actually to help the refrigerant vaporize and get into the system. Hopefully the oil goes along for the ride.
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Mark Johnson♦Aug 7 '14 at 17:17

The issue with this is that most cases of a car that have low freon is caused by a leak somewhere in the system.

If your car suddenly stopped blowing cold air, then this will most likely not fix your problem.

Your problem is probably one of two things:

A/C Compressor died

Large freon leak

I did a quick google and there appears to be A/C stop leak, but I do not know the efficacy of it, so YMMV. But, again, if you lost cold air quickly then this type of product most likely will not help you out.

From personal experience when the A/C stops working it is very often the compressor. There just isn't much else in the A/C system that is likely to break.

Stop leak compounds have a bad reputation and I avoid them, though I have no personal experience with them. I don't think I'd use them unless the whole system was about to be written off, say a suspected slow leak at the evaporator where the cost benefit analysis did not justify ripping into the dash to replace it.
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Mark Johnson♦May 28 '12 at 16:51